Flow Of Genetic Information

A gene is a segment of DNA that is located on a chromosome and that codes for a hereditary character. For example, a gene determines a person's hair color. The gene directs the making of the protein called melanin (a pigment) in hair follicle cells through an intermediate—the nucleic acid called ribonucleic acid, or RNA.

Figure 10-12 summarizes the flow of genetic information in a eukaryotic cell. During transcription, DNA acts as a template for the synthesis of RNA. In translation, RNA directs the assembly of proteins. Forming proteins based on information in DNA and carried out by RNA is called protein synthesis, or gene expression. This central concept can be symbolized as DNA —► RNA —► protein. Proteins do important work in cells, such as protecting the body against infections and carrying oxygen in red blood cells.

figure 10-12

DNA contains the instructions for building a protein. DNA transfers the instructions to an RNA molecule in a process called transcription. The RNA moves out into the cytoplasm, where its instructions are read and the protein is assembled in a process called translation.